The present invention relates to the marking of metal for tracking and identification purposes, and more particularly to imprinted metal tags which can be weld attached to metal workpieces.
Primary metal mills require that their products be accurately identified. Molten metal batches have unique "heat" (batch) chemistries that affect the mechanical properties of the ultimate (further formed) end products. Tracking the many individual pieces produced from a heat is a difficult, time consuming process with many opportunities for error in the stressful (hot, noisy, dimly lit, and physically dangerous) mill environment.
Metals first exit the molten heat as very hot (e.g., 1,800.degree. F. or 982.degree. C.) slabs or billets. Ideally, these slabs and billets should be identified with bar coded information immediately after they solidify and while they are still on the run out tables (before they can be mixed up). Automatic identification (e.g., bar codes) are preferred because they help eliminate the errors inherent in manual marking and reading (estimated by some to be as high as 1 in 300 attempts).
High temperature tags (some with bar codes) have been used for some time. For example, one commercial tag (supplied by Pannier Corp., Pittsburgh, Pa.) is a relatively thin (e.g. 0.008 in or 0.2032 mm thick) stainless steel tag which is coated with a high temperature white coating and is printable on-site using a dot matrix impact (inked ribbon) printer. These tags then are manually affixed to the slab or billet using a powder charged or pneumatically driven nail gun. Efforts to automate this prior art tag have generally not been successful because the dot matrix printer mechanism is "delicate" (dot matrix head and ribbon) and does not survive well in the vicinity of hot/dirty products; and the printer ribbon needs frequent replacement (e.g., every 300 tags), especially if high contrast bar codes are desired. Further, the nailing mechanism is difficult to automate as the environment is not conducive to bowl feeders. Nail "sticks" are limited to, say, 50 nails and stick feeds are unproved. Also, nailing becomes less acceptable (it is a foreign imperfection) and attachment is less reliable in premium (harder) grades of metal. Finally, nailing is increasingly unreliable as the product cools (hardens).
Another proposal is found in U.S. Pat. No. 5,422,167 that discloses a label that is formed from a sheet of metal having a face and a back. The sheet face is coated with a layer of paint that is resistant to temperature of the hot metal stock and receptive to being thermally transfer printed. The metal sheet label is of a thickness so that the paint layer can be thermally transfer printed using conventional markers designed for paper or films. The printed label is adapted to be attached to hot 1,200.degree. F. or 649.degree. C.) metal stock by welding bare (unpainted) zones of the label. This tag system can withstand the rigors of, for example, steel coil or "hot bands" production and can be attached by welding.
One acceptable solution to the problems identified is set forth in commonly-assigned U.S. Pat. No. 5,714,234 which is directed to a method for making a metal tag bearing visible indicia thereon that can be welded onto a substrate or workpiece. Such inventive method commences by providing a metal sheet having (1) a painted zone upon which is imprinted visible indicia, and (2) a bare metal zone, to form the tag. A preform is attached to the bare metal zone, preferably by welding. The preform has a depression adapted to receive weld wire for welding said tag to said metal workpiece. Preferably, the depression is a hole penetrating through the preform to the bare metal zone. The preform also is thicker than the metal tag, and of thickness effective for it being attached to metal by welding. The metal tag is attached to the workpiece by inserting a weld wire through the preform hole to make contact with the tag bare metal zone and welding the metal tag to said workpiece.
While such preform attachment approach in U.S. Pat. No. 5,714,234 represents a significant advancement in this field, there are certain disadvantages with it including cost, the need to remove coating from the area where the preforms are to be welded on, and the need for a spacer in the center of the tag to prevent its sagging. Thus, there still exists a need in the art for a tag and identification system that can withstand the rigors of primary metal mills and in which the tag production and affixation are automated in order to provide significant labor savings (e.g., at least 1 worker per shift) and to eliminate the errors resulting from manual application (e.g., shuffled tags, sequences out of step by one, and the like), and which overcomes the disadvantages inherent in the preform technology represented by U.S. Pat. No. 5,714,234.
Additionally, a variety of other raw and finished goods (e.g., automobile mechanical parts, tires, etc.) require marking for identification purposes. Such goods may be at or below room temperature when the marking requirement arises. A system that has the flexibility to mark "hot" metal as well as lower temperature items would be welcome.